Towers of this type may be several hundred feet in height with a diameter at the base being somewhat greater than one-third the height of the tower. Effluent water is pumped into the interior of the tower at an intermediate level is thereby brought into contact with an upwardly flowing draft of atmospheric air developed by natural wind current which are introduced at the base of the tower.
Contact between the air and water in the tower is maintained in one of two ways. The tower may be filled with rock fragments or may include a lattice-work matrix through which the air current passes to evaporate and cool the water which is continually sprayed on the rock or matrix surfaces. Due to the restriction in the flow of air only a minimum of power can be generated by wind turbines placed in the air stream.
Generally, when the generation of power as an ancillary benefit is considered, an unimpeded air draft in the tower is required and water is supplied by nozzles arranged around the interior wall of the tower near the base to minimize the amount of water lost as evaporated vapor.
In one form of cooling tower of this type, a wind turbine using propellor blades rotating on a vertical axis was placed in the exit plane of the tower. However, it was found that the blades interferred with the tower's natural drafting ability especially when the velocity of the air draft at the exit plane was in the range of 12-15 ft/sec or less.
It has also been suggested to use a tower having a hyperbolic vertical wall configuration in which the horizontal cross-section converges upwardly from the base to an intermediate level and then diverges to the exit plane at the top, with the vertically rotating blades of the wind turbine located at the narrow throat portion to maximize the increased air velocity at that level since power is proportional to the air velocity cubed, and additional power should be obtained by the vortex core formed in the exhaust draft above the turbine. However, the reduction in throat diameter needed to increase the air velocity resulted in an excessive air flow pressure drop which reduced the air flow. The result was that a minimal increase in power output was accompanied by excessive costs in additional wind turbine support structures.
U.S. Pat. No. 4,031,173 issued to Paul Rogers discloses a tower having an arrangement of blade-like surfaces mounted on the exterior of the tower for rotation about the tower in a horizontal plane in response to wind movement. Each of the blades is adjustably mounted in a framework carried on rollers supported on a track that surrounds the tower. The complexity of this design would tend to make it commercially impractical.
U.S. Pat. No. 4,070,131, issued to James T. Yen discloses two forms of towers in which a vortex core air flow with a wind turbine rotating in a horizontal plane located at the base of the tower. In one form of the invention the tower wall consists of a series of narrow vertical vanes mounted for individual rotation under the control of a wind direction sensor for the purpose of introducing wind into the tower with a swirling movement regardless of the direction from which the wind is arriving.
In a modified form a single wind inlet includes a helical passage at the base of the tower to introduce air with a swirling motion and the entire tower and single air inlet are mounted on a rotary platform for movement, under control of a wind direction sensor, to place the inlet in correct position at all times. Nevertheless, the concept of building a tower several hundred feet tall and nearly as wide at its base with the walls consisting of automatically pivoted narrow air-directing vases or of building a solid-walled tower of that size and mounting it and its attendant air inlet and power generating mechanisms on a rotatable platform are not presently commercially appealing. It should also be mentioned that no specific provision for cooling water is disclosed in this patent.